(a) Field of the Invention
The invention relates to improvements to a television color generator. More specifically, the invention relates to a novel phase shifting circuit for such a color generator.
(b) Description of Prior Art
Systems for generating color signals for television are typically complex. For example, systems for generating a PAL color signal use balanced generators and sine/cosine generators. These systems have balance problems and therefore require many adjustments.
Other systems are also known in the prior art which is exemplified by, for example, U.S. Pat. No. 4,329,710, Taylor, issued May 11, 1982; U.S. Pat. No. 4,051,520, Davidse et al, issued Sept. 27, 1977; U.S. Pat. No. 4,040,086, Wellhausen et al, issued Aug. 2, 1977; and U.S. Pat. No. 4,003,078, Owen, issued Jan. 11, 1977. The '078 patent teaches an arrangement for providing time delay to a sub-carrier whereby to shift the phase of that sub-carrier. The arrangement uses a plurality of monostable vibrators. However, this circuit is an open loop arrangement. Because it is open loop, it could not accurately generate the two required phases for a PAL system. Although it might be possible to use the patented circuit in a PAL system with accuracy sacrificed, such an open loop approach would not be stable or easy to adjust.